I have attempted to update one of my two installations on my Windows IIS7 web server concluding with failure by both using the auto update feature and the manual update feature. I have followed the guides in the WordPress documentation, both standard manual install and extended and also read the "most common issues". The update appears to be successful at first, but then reroutes to a 500 error for every page after the install dialog page, it even says it's successful before rerouting.
I have a full directory backup of the installation, unfortunately I do not have a DB backup any older then 6 days from today. When I restore the full file backup, by either merging or completely replacing the root WordPress install directory, I browse any page and WordPress asks me to update the database. I do the update and all is working again at 3.1.1, leaving me to once again update with failure either manually or automagically. What is the issue? Cannot seem to figure out what is causing this issue. Any help is much appreciated.